The statements in this section merely provide background information related to the present disclosure. Accordingly, such statements are not intended to constitute an admission of prior art.
Diesel engines manage air-fuel ratios (AFR), pressure and temperature to achieve robust combustion. An oxygen sensor, e.g., lambda sensor, disposed in an exhaust gas feedstream output from an engine is commonly employed for providing feedback control for the AFR of the engine to reduce vehicle emissions by ensuring that the engine is efficiently combusting fuel. The measurement provided by the oxygen sensor is a difference between the amount of oxygen in the exhaust gas feedstream and an oxygen content of ambient air. It is known, for example, to assume an ideal oxygen content of ambient air to be 20.95%. However, an actual oxygen content of ambient air varies due to humidity. For instance, as humidity increases the oxygen content of ambient air decreases to values lower than 20.95%.
It is known to employ fuel set point adaptation by adjusting boost to the engine and external exhaust gas recirculation to the engine. Fuel set point adaptation strategies are dependent upon feedback provided by the oxygen sensor, e.g., lambda sensor. Errors in the fuel set point adaptation strategies can result when the ideal oxygen content of ambient air is assumed without taking into account humidity.
It is known to employ a fuel injection system for injecting fuel into the engine. The fuel system utilizes fuel injectors which require an energizing time to inject a fuel mass into the engine. Over the life of the vehicle, energizing times are required to be increased to maintain a desired injected fuel mass. It is known to offset or adjust a predetermined energizing time based on feedback provided by the oxygen sensor during each drive cycle. However, this offset or adjustment to the predetermined energizing time can result in an error when the ideal oxygen content of ambient air is assumed without taking into account variations in humidity.
It is known that deterioration of sensing elements of the oxygen sensor occur over time resulting in oxygen sensor aging where the oxygen sensor becomes less sensitive to oxygen over time. Learned offsets can be employed to the feedback provided by the oxygen sensor to account for oxygen sensor aging. However, these learned offsets can result in an error when the ideal oxygen content of ambient air is assumed without taking into account variations in humidity.